A typical vehicle seat belt system includes seat belt webbing extensible about a vehicle occupant for helping to restrain the occupant in the event of a vehicle crash condition. It is known to use a pretensioner to apply a force to the seat belt in the event of a vehicle crash condition. Typically, the pretensioner includes a pyrotechnic device that is actuated when a crash condition is sensed. A known pretensioner described in U.S. Patent Application Publication No. 2007/0241550 includes a flexible drive member.